A comprehensive examination of basal insulin levels and insulin responses to oral glucose loading has been carried out in 472 men and 299 women aged 20 to 96 years. Men had significantly lower body fat content than women, but higher plasma glucose levels, and a much higher waist/hip ratio. Both fasting and past-glucose insulin levels were higher in men, but when adjusted for the sex differences in obesity and glucose levels, this sex difference disappeared. Insulin levels fell progressively with age even when "corrected" for differences in body composition and glucose variables, from 323 pM to 267, 253, and 228 in young (20-39 yr) middle-aged, old, and very old (80-96 yr) individuals. Thus the decline in insulin response cannot be attributed to other age-associated changes. In essence, this demonstrates that a defect in insulin secretion occurs in addition to the previously demonstrated defect in insulin sensitivity with aging. Data from the 30 year experience of the BLSA were used to provide the evidence needed to remove the upper age limit from the collaborative clinical trial on prevention of diabetes (conversion of subjects from Impaired Glucose Tolerance (IGT) to WHO-classifiable Diabetes Mellitus. The BLSA data set provides the most extensive experience on Caucasian subjects across the adult span of years. Data provided include: (1) conversion rates as modified by sex, BMI, fasting glucose, glucose tolerance, and family history of diabetes; (2) incidence rates of development of coronary heart disease in IGT; (3) conversion formulae of plasma creatinine levels to 24-hr creatinine clearance for potential dry studies; (4) mortality rates in IGT subjects compared to those with normal glucose tolerance. Data from BLSA participants on incidence of development of diabetes are included in a publication under the auspices of the Diabetes Prevention Program which examines this incidence rate as influenced by age, sex, and race in a summary of the several studies that provide reliable incidence data from various ethnic groups world-wide.